askrene: move fork() entry point into its own file.

diff --git a/plugins/askrene/Makefile b/plugins/askrene/Makefile
index 3c3f5c4b..fd8e9f51 100644
--- a/plugins/askrene/Makefile
+++ b/plugins/askrene/Makefile
@@ -5,6 +5,7 @@ PLUGIN_ASKRENE_PARENT_SRC := \
 	plugins/askrene/reserve.c \
 
 PLUGIN_ASKRENE_CHILD_SRC := \
+	plugins/askrene/child/entry.c \
 	plugins/askrene/child/mcf.c \
 	plugins/askrene/child/dijkstra.c \
 	plugins/askrene/child/flow.c \
diff --git a/plugins/askrene/askrene.c b/plugins/askrene/askrene.c
index 8a4c009d..bbbae51e 100644
--- a/plugins/askrene/askrene.c
+++ b/plugins/askrene/askrene.c
@@ -8,9 +8,6 @@
  */
 #include "config.h"
 #include <ccan/array_size/array_size.h>
-#include <ccan/json_out/json_out.h>
-#include <ccan/noerr/noerr.h>
-#include <ccan/read_write_all/read_write_all.h>
 #include <ccan/tal/grab_file/grab_file.h>
 #include <ccan/tal/str/str.h>
 #include <common/clock_time.h>
@@ -26,17 +23,12 @@
 #include <math.h>
 #include <plugins/askrene/askrene.h>
 #include <plugins/askrene/child/child_log.h>
-#include <plugins/askrene/child/flow.h>
-#include <plugins/askrene/child/mcf.h>
+#include <plugins/askrene/child/entry.h>
 #include <plugins/askrene/layer.h>
 #include <plugins/askrene/reserve.h>
 #include <sys/wait.h>
-#include <unistd.h>
 #include <wire/wire_sync.h>
 
-/* Temporary hack */
-static bool am_child = false;
-
 /* "spendable" for a channel assumes a single HTLC: for additional HTLCs,
  * the need to pay for fees (if we're the owner) reduces it */
 struct per_htlc_cost {
@@ -340,27 +332,6 @@ const char *rq_log(const tal_t *ctx,
 	return msg;
 }
 
-static const char *fmt_route(const tal_t *ctx,
-			     const struct route *route,
-			     struct amount_msat delivers,
-			     u32 final_cltv)
-{
-	char *str = tal_strdup(ctx, "");
-
-	for (size_t i = 0; i < tal_count(route->hops); i++) {
-		struct short_channel_id_dir scidd;
-		scidd.scid = route->hops[i].scid;
-		scidd.dir = route->hops[i].direction;
-		tal_append_fmt(&str, "%s/%u %s -> ",
-			       fmt_amount_msat(tmpctx, route->hops[i].amount),
-			       route->hops[i].delay,
-			       fmt_short_channel_id_dir(tmpctx, &scidd));
-	}
-	tal_append_fmt(&str, "%s/%u",
-		       fmt_amount_msat(tmpctx, delivers), final_cltv);
-	return str;
-}
-
 enum algorithm {
 	/* Min. Cost Flow by successive shortests paths. */
 	ALGO_DEFAULT,
@@ -439,133 +410,6 @@ static void apply_layers(struct askrene *askrene, struct route_query *rq,
 	}
 }
 
-/* Convert back into routes, with delay and other information fixed */
-static struct route **convert_flows_to_routes(const tal_t *ctx,
-					      struct route_query *rq,
-					      u32 finalcltv,
-					      struct flow **flows,
-					      struct amount_msat **amounts,
-					      bool include_fees)
-{
-	struct route **routes;
-	routes = tal_arr(ctx, struct route *, tal_count(flows));
-	*amounts = tal_arr(ctx, struct amount_msat, tal_count(flows));
-
-	for (size_t i = 0; i < tal_count(flows); i++) {
-		struct route *r;
-		struct amount_msat msat;
-		u32 delay;
-
-		routes[i] = r = tal(routes, struct route);
-		r->success_prob = flow_probability(flows[i], rq);
-		r->hops = tal_arr(r, struct route_hop, tal_count(flows[i]->path));
-
-		msat = flows[i]->delivers;
-		delay = finalcltv;
-
-		if (!include_fees) {
-			/* Fill in backwards to calc amount and delay */
-			for (int j = tal_count(flows[i]->path) - 1; j >= 0;
-			     j--) {
-				struct route_hop *rh = &r->hops[j];
-				struct gossmap_node *far_end;
-				const struct half_chan *h =
-				    flow_edge(flows[i], j);
-
-				if (!amount_msat_add_fee(&msat, h->base_fee,
-							 h->proportional_fee))
-					plugin_err(rq->plugin,
-						   "Adding fee to amount");
-				delay += h->delay;
-
-				rh->scid = gossmap_chan_scid(rq->gossmap,
-							     flows[i]->path[j]);
-				rh->direction = flows[i]->dirs[j];
-				far_end = gossmap_nth_node(rq->gossmap,
-							   flows[i]->path[j],
-							   !flows[i]->dirs[j]);
-				gossmap_node_get_id(rq->gossmap, far_end,
-						    &rh->node_id);
-				rh->amount = msat;
-				rh->delay = delay;
-			}
-		        (*amounts)[i] = flows[i]->delivers;
-		} else {
-			/* Fill in backwards to calc delay */
-			for (int j = tal_count(flows[i]->path) - 1; j >= 0;
-			     j--) {
-				struct route_hop *rh = &r->hops[j];
-				struct gossmap_node *far_end;
-				const struct half_chan *h =
-				    flow_edge(flows[i], j);
-
-				delay += h->delay;
-
-				rh->scid = gossmap_chan_scid(rq->gossmap,
-							     flows[i]->path[j]);
-				rh->direction = flows[i]->dirs[j];
-				far_end = gossmap_nth_node(rq->gossmap,
-							   flows[i]->path[j],
-							   !flows[i]->dirs[j]);
-				gossmap_node_get_id(rq->gossmap, far_end,
-						    &rh->node_id);
-				rh->delay = delay;
-			}
-			/* Compute fees forward */
-			for (int j = 0; j < tal_count(flows[i]->path); j++) {
-				struct route_hop *rh = &r->hops[j];
-				const struct half_chan *h =
-				    flow_edge(flows[i], j);
-
-				rh->amount = msat;
-                                msat = amount_msat_sub_fee(msat, h->base_fee,
-							   h->proportional_fee);
-			}
-		        (*amounts)[i] = msat;
-		}
-
-		rq_log(tmpctx, rq, LOG_INFORM, "Flow %zu/%zu: %s",
-		       i, tal_count(flows),
-		       fmt_route(tmpctx, r, (*amounts)[i], finalcltv));
-	}
-
-	return routes;
-}
-
-static void json_add_getroutes(struct json_stream *js,
-			       struct route **routes,
-			       const struct amount_msat *amounts,
-			       double probability,
-			       u32 final_cltv)
-{
-	json_add_u64(js, "probability_ppm", (u64)(probability * 1000000));
-	json_array_start(js, "routes");
-	for (size_t i = 0; i < tal_count(routes); i++) {
-		json_object_start(js, NULL);
-		json_add_u64(js, "probability_ppm",
-			     (u64)(routes[i]->success_prob * 1000000));
-		json_add_amount_msat(js, "amount_msat", amounts[i]);
-		json_add_u32(js, "final_cltv", final_cltv);
-		json_array_start(js, "path");
-		for (size_t j = 0; j < tal_count(routes[i]->hops); j++) {
-			struct short_channel_id_dir scidd;
-			const struct route_hop *r = &routes[i]->hops[j];
-			json_object_start(js, NULL);
-			scidd.scid = r->scid;
-			scidd.dir = r->direction;
-			json_add_short_channel_id_dir(
-			    js, "short_channel_id_dir", scidd);
-			json_add_node_id(js, "next_node_id", &r->node_id);
-			json_add_amount_msat(js, "amount_msat", r->amount);
-			json_add_u32(js, "delay", r->delay);
-			json_object_end(js);
-		}
-		json_array_end(js);
-		json_object_end(js);
-	}
-	json_array_end(js);
-}
-
 void get_constraints(const struct route_query *rq,
 		     const struct gossmap_chan *chan,
 		     int dir,
@@ -602,111 +446,6 @@ void get_constraints(const struct route_query *rq,
 	reserve_sub(rq->reserved, &scidd, rq->layers, max);
 }
 
-/* Returns fd to child */
-static int fork_router_child(struct route_query *rq,
-			     enum algorithm algo,
-			     struct timemono deadline,
-			     const struct gossmap_node *srcnode,
-			     const struct gossmap_node *dstnode,
-			     struct amount_msat amount,
-			     struct amount_msat maxfee,
-			     u32 finalcltv, u32 maxdelay,
-			     bool include_fees,
-			     const char *cmd_id,
-			     struct json_filter *cmd_filter,
-			     int *log_fd,
-			     int *child_pid)
-{
-	int replyfds[2], logfds[2];
-	double probability;
-	struct flow **flows;
-	struct route **routes;
-	struct amount_msat *amounts;
-	const char *err, *p;
-	size_t len;
-
-	if (pipe(replyfds) != 0)
-		return -1;
-	if (pipe(logfds) != 0) {
-		close_noerr(replyfds[0]);
-		close_noerr(replyfds[1]);
-		return -1;
-	}
-	*child_pid = fork();
-	if (*child_pid < 0) {
-		close_noerr(replyfds[0]);
-		close_noerr(replyfds[1]);
-		close_noerr(logfds[0]);
-		close_noerr(logfds[1]);
-		return -1;
-	}
-	if (*child_pid != 0) {
-		close(logfds[1]);
-		close(replyfds[1]);
-		*log_fd = logfds[0];
-		return replyfds[0];
-	}
-
-	/* We are the child.  Run the algo */
-	close(logfds[0]);
-	close(replyfds[0]);
-	set_child_log_fd(logfds[1]);
-	am_child = true;
-	if (algo == ALGO_SINGLE_PATH) {
-		err = single_path_routes(rq, rq, deadline, srcnode, dstnode,
-					 amount, maxfee, finalcltv,
-					 maxdelay, &flows, &probability);
-	} else {
-		assert(algo == ALGO_DEFAULT);
-		err = default_routes(rq, rq, deadline, srcnode, dstnode,
-				     amount, maxfee, finalcltv, maxdelay,
-				     &flows, &probability);
-	}
-	if (err) {
-		write_all(replyfds[1], err, strlen(err));
-		/* Non-zero exit tells parent this is an error string. */
-		exit(1);
-	}
-
-	/* otherwise we continue */
-	assert(tal_count(flows) > 0);
-	rq_log(tmpctx, rq, LOG_DBG, "Final answer has %zu flows",
-	       tal_count(flows));
-
-	/* convert flows to routes */
-	routes = convert_flows_to_routes(rq, rq, finalcltv, flows,
-					 &amounts, include_fees);
-	assert(tal_count(routes) == tal_count(flows));
-	assert(tal_count(amounts) == tal_count(flows));
-
-	/* output the results */
-	struct json_stream *js = new_json_stream(tmpctx, NULL, NULL);
-	json_object_start(js, NULL);
-	json_add_string(js, "jsonrpc", "2.0");
-	json_add_id(js, cmd_id);
-	json_object_start(js, "result");
-	if (cmd_filter)
-		json_stream_attach_filter(js, cmd_filter);
-	json_add_getroutes(js, routes, amounts, probability, finalcltv);
-
-	/* Detach filter before it complains about closing object it never saw */
-	if (cmd_filter) {
-		err = json_stream_detach_filter(tmpctx, js);
-		if (err)
-			json_add_string(js, "warning_parameter_filter", err);
-	}
-	/* "result" object */
-	json_object_end(js);
-	/* Global object */
-	json_object_end(js);
-	json_stream_close(js, NULL);
-
-	p = json_out_contents(js->jout, &len);
-	if (!write_all(replyfds[1], p, len))
-		abort();
-	exit(0);
-}
-
 static void process_child_logs(struct route_query *rq, int log_fd)
 {
 	u8 *msg;
@@ -841,7 +580,7 @@ static struct command_result *do_getroutes(struct command *cmd,
 	time_start = time_mono();
 	deadline = timemono_add(time_start,
 				time_from_sec(askrene->route_seconds));
-	child_fd = fork_router_child(rq, info->dev_algo,
+	child_fd = fork_router_child(rq, info->dev_algo == ALGO_SINGLE_PATH,
 				     deadline, srcnode, dstnode, info->amount,
 				     info->maxfee, info->finalcltv, info->maxdelay,
 				     include_fees,
diff --git a/plugins/askrene/askrene.h b/plugins/askrene/askrene.h
index c9b15e39..85acc650 100644
--- a/plugins/askrene/askrene.h
+++ b/plugins/askrene/askrene.h
@@ -12,14 +12,6 @@
 
 struct gossmap_chan;
 
-/* A single route. */
-struct route {
-	/* Actual path to take */
-	struct route_hop *hops;
-	/* Probability estimate (0-1) */
-	double success_prob;
-};
-
 /* Grab-bag of "globals" for this plugin */
 struct askrene {
 	struct plugin *plugin;
diff --git a/plugins/askrene/child/entry.c b/plugins/askrene/child/entry.c
new file mode 100644
index 00000000..246a4a51
--- /dev/null
+++ b/plugins/askrene/child/entry.c
@@ -0,0 +1,279 @@
+#include "config.h"
+#include <assert.h>
+#include <ccan/json_out/json_out.h>
+#include <ccan/noerr/noerr.h>
+#include <ccan/read_write_all/read_write_all.h>
+#include <ccan/tal/str/str.h>
+#include <common/json_stream.h>
+#include <common/route.h>
+#include <common/utils.h>
+#include <plugins/askrene/askrene.h>
+#include <plugins/askrene/child/child_log.h>
+#include <plugins/askrene/child/entry.h>
+#include <plugins/askrene/child/flow.h>
+#include <plugins/askrene/child/mcf.h>
+#include <unistd.h>
+
+/* Temporary hack */
+bool am_child = false;
+
+/* A single route. */
+struct route {
+	/* Actual path to take */
+	struct route_hop *hops;
+	/* Probability estimate (0-1) */
+	double success_prob;
+};
+
+static const char *fmt_route(const tal_t *ctx,
+			     const struct route *route,
+			     struct amount_msat delivers,
+			     u32 final_cltv)
+{
+	char *str = tal_strdup(ctx, "");
+
+	for (size_t i = 0; i < tal_count(route->hops); i++) {
+		struct short_channel_id_dir scidd;
+		scidd.scid = route->hops[i].scid;
+		scidd.dir = route->hops[i].direction;
+		tal_append_fmt(&str, "%s/%u %s -> ",
+			       fmt_amount_msat(tmpctx, route->hops[i].amount),
+			       route->hops[i].delay,
+			       fmt_short_channel_id_dir(tmpctx, &scidd));
+	}
+	tal_append_fmt(&str, "%s/%u",
+		       fmt_amount_msat(tmpctx, delivers), final_cltv);
+	return str;
+}
+
+/* Convert back into routes, with delay and other information fixed */
+static struct route **convert_flows_to_routes(const tal_t *ctx,
+					      struct route_query *rq,
+					      u32 finalcltv,
+					      struct flow **flows,
+					      struct amount_msat **amounts,
+					      bool include_fees)
+{
+	struct route **routes;
+	routes = tal_arr(ctx, struct route *, tal_count(flows));
+	*amounts = tal_arr(ctx, struct amount_msat, tal_count(flows));
+
+	for (size_t i = 0; i < tal_count(flows); i++) {
+		struct route *r;
+		struct amount_msat msat;
+		u32 delay;
+
+		routes[i] = r = tal(routes, struct route);
+		r->success_prob = flow_probability(flows[i], rq);
+		r->hops = tal_arr(r, struct route_hop, tal_count(flows[i]->path));
+
+		msat = flows[i]->delivers;
+		delay = finalcltv;
+
+		if (!include_fees) {
+			/* Fill in backwards to calc amount and delay */
+			for (int j = tal_count(flows[i]->path) - 1; j >= 0;
+			     j--) {
+				struct route_hop *rh = &r->hops[j];
+				struct gossmap_node *far_end;
+				const struct half_chan *h =
+				    flow_edge(flows[i], j);
+
+				if (!amount_msat_add_fee(&msat, h->base_fee,
+							 h->proportional_fee))
+					plugin_err(rq->plugin,
+						   "Adding fee to amount");
+				delay += h->delay;
+
+				rh->scid = gossmap_chan_scid(rq->gossmap,
+							     flows[i]->path[j]);
+				rh->direction = flows[i]->dirs[j];
+				far_end = gossmap_nth_node(rq->gossmap,
+							   flows[i]->path[j],
+							   !flows[i]->dirs[j]);
+				gossmap_node_get_id(rq->gossmap, far_end,
+						    &rh->node_id);
+				rh->amount = msat;
+				rh->delay = delay;
+			}
+		        (*amounts)[i] = flows[i]->delivers;
+		} else {
+			/* Fill in backwards to calc delay */
+			for (int j = tal_count(flows[i]->path) - 1; j >= 0;
+			     j--) {
+				struct route_hop *rh = &r->hops[j];
+				struct gossmap_node *far_end;
+				const struct half_chan *h =
+				    flow_edge(flows[i], j);
+
+				delay += h->delay;
+
+				rh->scid = gossmap_chan_scid(rq->gossmap,
+							     flows[i]->path[j]);
+				rh->direction = flows[i]->dirs[j];
+				far_end = gossmap_nth_node(rq->gossmap,
+							   flows[i]->path[j],
+							   !flows[i]->dirs[j]);
+				gossmap_node_get_id(rq->gossmap, far_end,
+						    &rh->node_id);
+				rh->delay = delay;
+			}
+			/* Compute fees forward */
+			for (int j = 0; j < tal_count(flows[i]->path); j++) {
+				struct route_hop *rh = &r->hops[j];
+				const struct half_chan *h =
+				    flow_edge(flows[i], j);
+
+				rh->amount = msat;
+                                msat = amount_msat_sub_fee(msat, h->base_fee,
+							   h->proportional_fee);
+			}
+		        (*amounts)[i] = msat;
+		}
+
+		child_log(tmpctx, LOG_INFORM, "Flow %zu/%zu: %s",
+			  i, tal_count(flows),
+			  fmt_route(tmpctx, r, (*amounts)[i], finalcltv));
+	}
+
+	return routes;
+}
+
+static void json_add_getroutes(struct json_stream *js,
+			       struct route **routes,
+			       const struct amount_msat *amounts,
+			       double probability,
+			       u32 final_cltv)
+{
+	json_add_u64(js, "probability_ppm", (u64)(probability * 1000000));
+	json_array_start(js, "routes");
+	for (size_t i = 0; i < tal_count(routes); i++) {
+		json_object_start(js, NULL);
+		json_add_u64(js, "probability_ppm",
+			     (u64)(routes[i]->success_prob * 1000000));
+		json_add_amount_msat(js, "amount_msat", amounts[i]);
+		json_add_u32(js, "final_cltv", final_cltv);
+		json_array_start(js, "path");
+		for (size_t j = 0; j < tal_count(routes[i]->hops); j++) {
+			struct short_channel_id_dir scidd;
+			const struct route_hop *r = &routes[i]->hops[j];
+			json_object_start(js, NULL);
+			scidd.scid = r->scid;
+			scidd.dir = r->direction;
+			json_add_short_channel_id_dir(
+			    js, "short_channel_id_dir", scidd);
+			json_add_node_id(js, "next_node_id", &r->node_id);
+			json_add_amount_msat(js, "amount_msat", r->amount);
+			json_add_u32(js, "delay", r->delay);
+			json_object_end(js);
+		}
+		json_array_end(js);
+		json_object_end(js);
+	}
+	json_array_end(js);
+}
+
+
+/* Returns fd to child */
+int fork_router_child(struct route_query *rq,
+		      bool single_path,
+		      struct timemono deadline,
+		      const struct gossmap_node *srcnode,
+		      const struct gossmap_node *dstnode,
+		      struct amount_msat amount, struct amount_msat maxfee,
+		      u32 finalcltv, u32 maxdelay,
+		      bool include_fees,
+		      const char *cmd_id,
+		      struct json_filter *cmd_filter,
+		      int *log_fd,
+		      int *child_pid)
+{
+	int replyfds[2], logfds[2];
+	double probability;
+	struct flow **flows;
+	struct route **routes;
+	struct amount_msat *amounts;
+	const char *err, *p;
+	size_t len;
+
+	if (pipe(replyfds) != 0)
+		return -1;
+	if (pipe(logfds) != 0) {
+		close_noerr(replyfds[0]);
+		close_noerr(replyfds[1]);
+		return -1;
+	}
+	*child_pid = fork();
+	if (*child_pid < 0) {
+		close_noerr(replyfds[0]);
+		close_noerr(replyfds[1]);
+		close_noerr(logfds[0]);
+		close_noerr(logfds[1]);
+		return -1;
+	}
+	if (*child_pid != 0) {
+		close(logfds[1]);
+		close(replyfds[1]);
+		*log_fd = logfds[0];
+		return replyfds[0];
+	}
+
+	/* We are the child.  Run the algo */
+	close(logfds[0]);
+	close(replyfds[0]);
+	set_child_log_fd(logfds[1]);
+	am_child = true;
+	if (single_path) {
+		err = single_path_routes(rq, rq, deadline, srcnode, dstnode,
+					 amount, maxfee, finalcltv,
+					 maxdelay, &flows, &probability);
+	} else {
+		err = default_routes(rq, rq, deadline, srcnode, dstnode,
+				     amount, maxfee, finalcltv, maxdelay,
+				     &flows, &probability);
+	}
+	if (err) {
+		write_all(replyfds[1], err, strlen(err));
+		/* Non-zero exit tells parent this is an error string. */
+		exit(1);
+	}
+
+	/* otherwise we continue */
+	assert(tal_count(flows) > 0);
+	child_log(tmpctx, LOG_DBG, "Final answer has %zu flows",
+		  tal_count(flows));
+
+	/* convert flows to routes */
+	routes = convert_flows_to_routes(rq, rq, finalcltv, flows,
+					 &amounts, include_fees);
+	assert(tal_count(routes) == tal_count(flows));
+	assert(tal_count(amounts) == tal_count(flows));
+
+	/* output the results */
+	struct json_stream *js = new_json_stream(tmpctx, NULL, NULL);
+	json_object_start(js, NULL);
+	json_add_string(js, "jsonrpc", "2.0");
+	json_add_id(js, cmd_id);
+	json_object_start(js, "result");
+	if (cmd_filter)
+		json_stream_attach_filter(js, cmd_filter);
+	json_add_getroutes(js, routes, amounts, probability, finalcltv);
+
+	/* Detach filter before it complains about closing object it never saw */
+	if (cmd_filter) {
+		err = json_stream_detach_filter(tmpctx, js);
+		if (err)
+			json_add_string(js, "warning_parameter_filter", err);
+	}
+	/* "result" object */
+	json_object_end(js);
+	/* Global object */
+	json_object_end(js);
+	json_stream_close(js, NULL);
+
+	p = json_out_contents(js->jout, &len);
+	if (!write_all(replyfds[1], p, len))
+		abort();
+	exit(0);
+}
+
diff --git a/plugins/askrene/child/entry.h b/plugins/askrene/child/entry.h
new file mode 100644
index 00000000..2ea790a4
--- /dev/null
+++ b/plugins/askrene/child/entry.h
@@ -0,0 +1,29 @@
+#ifndef LIGHTNING_PLUGINS_ASKRENE_CHILD_ENTRY_H
+#define LIGHTNING_PLUGINS_ASKRENE_CHILD_ENTRY_H
+#include "config.h"
+#include <ccan/short_types/short_types.h>
+#include <ccan/time/time.h>
+#include <common/amount.h>
+#include <stdbool.h>
+
+struct route_query;
+struct gossmap_node;
+struct json_filter;
+
+/* Entry point to the child process. */
+int fork_router_child(struct route_query *rq,
+		      bool single_path,
+		      struct timemono deadline,
+		      const struct gossmap_node *srcnode,
+		      const struct gossmap_node *dstnode,
+		      struct amount_msat amount, struct amount_msat maxfee,
+		      u32 finalcltv, u32 maxdelay,
+		      bool include_fees,
+		      const char *cmd_id,
+		      struct json_filter *cmd_filter,
+		      int *log_fd,
+		      int *child_pid);
+
+/* FIXME: Remove this */
+extern bool am_child;
+#endif /* LIGHTNING_PLUGINS_ASKRENE_CHILD_ENTRY_H */